Research On The Control Strategy For MMC Based Statcom

With the development of our society, increasing use of electricity leads toincreasing grid load, which results in increasing reactive power demand, reducinggrid power factor, weakened power supply capability and decreasing economicbenefit. So high power quality and reliable power supply become the most importantissue in power system.Modular multilevel converter, because of its DC bus topology and highmodular, can be easily equipped and operated in four quadrants. It has vitalsignificance in STATCOM research. The paper mainly did research into the controlstrategy for MMC based STATCOM and experiment platform.The paper firstly analyzed the principle and control algorithm of MMC basedSTATCOM. By summarizing the advantage and disadvantage of conventionalpre-charging method for MMC, a new method making use of AC grid to chargeMMC based STATCOM was proposed. Because of independent module andnonideal components, DC capacitor voltage unbalance and ripple are caused easily.For this problem, a capacitor voltage balance method combing with modulationmethod was proposed. Finally method based on d-q transformation was adopted tocontrol both DC bus voltage and current.Then the paper designed and set up9-level experiment platform. The workincluded the selection of parameter and the design of circuit. Because the number ofboth modular and signal was large, the system used DSP as well as FPGA as maincontroller. In the sub-modular, ARM was used to collect, store and transmit signals.Sub-module and main control board exchange information by use of CAN bus.Finally, the control strategies were verified. A9-level simulation model was setup in PSCAD. The simulation result was in accordance with theoretical analysis.The program of DSP and FPGA was done to realize the control of the platform,verifying the voltage balance control strategy in the condition of non-load,inductance load and grid-connection. The experiment result was ideal.